My design is for an offroad camper but with a 5' wide body and 10.5" wide tyres (Oz spelling there

) I'm concerned about the overall track width, I'd like to keep it the same as the Jeep. I'm thinking of recessing the tyres in so that the width at the internal wheel wells is 4', now I like a bit of room in bed and the TD is for two, is 4' wide enough around the legs. It's 49" down from the front of the TD which I guess puts it around the knees. Will I be smacking my knees all the time and regret not just puting up with a track wider than the Jeep?
I'm also going to try and keep the interior wheel arches as low as possible (they are quite high in this pic) and try and do it so I at least get an inch or two of matress over the top of them. Any other suggestions other than smaller tyres
Cheers
Steve